Heat exchangers have been used in medical, automotive, and industrial applications. Their efficiency and heat transfer capacity are determined by the thermal conductivity, flow distribution, and heat transfer surface area of the exchanger.
Examples of applications of heat exchanger use in semiconductor manufacturing where controlled heating of a liquid is often required include: sulfuric acid and hydrogen peroxide photoresist strip solutions, hot phosphoric acid baths for silicon nitride and aluminum metal etching, ammonium hydroxide and hydrogen peroxide SC1 cleaning solutions, hydrochloric acid and hydrogen peroxide SC2 cleaning solutions, hot deionized water rinses, and heated organic amine based photoresist strippers.
Heating of chemical mechanical planarization, CMP, liquids and abrasive slurries can also be performed to control removal rates. A chemical mechanical slurry typically comprises solid abrasive materials like alumina or silica abrasives, oxidizers like hydrogen peroxide, and either acids or bases such as hydrochloric acid or ammonium hydroxide.
In many semiconductor manufacturing steps liquids with accurately controlled temperature are dispensed onto substrates to form thin films. In these applications the temperature of the liquid has an effect on the uniformity and thickness of the final film.
Accurate and repeatable temperature conditioning of liquids such as spin on dielectrics, photoresists, antireflective coatings, and developers prior to dispense onto a stationary or spinning substrate requires heating or cooling of these liquids. This is often done by flowing the process liquid inside a relatively thick walled perfluorinated tube whose temperature is controlled on the outside of the tube with a flow of water.
Heat exchangers are devices which transfer energy between fluids. This is done by contacting one fluid, the process fluid, and a working fluid or exchange fluid. These two fluids are physically separated from each other by the walls the material comprising the heat exchanger. Polymer based heat exchangers are commonly used for heating and cooling chemicals for many these applications due to its chemical inertness, high purity, and resistance to corrosion. However polymeric heat exchange devices are usually large because a large heat transfer surface area is required to effect a given temperature change due to the low thermal conductivity of the polymers used in the device. Such a large size has not made it practical to use such devices on semiconductor process tools
Gas to liquid finned heat exchangers are used in conditioning gases used in lasers. These exchangers are commonly made of metals which are not suitable for use with corrosive chemicals or gases and can produce particles when moisture is present.
U.S. Pat. No. 3,315,740 discloses a method of bonding tubes together by fusion for use in heat exchangers. Tubes of a thermoplastic material are gathered in a manner such that the end portions of the tubes are in a contacting parallel relationship. Canadian Patent 1252082 teaches the art of making spiral wound polymeric heat exchangers and U.S. Pat. No. 4,980,060 describes fusion bonded potting of porous hollow fiber tubes for filtration. Neither disclosure contemplates the use of temperature control of such devices.
U.S. Pat. No. 5,216,743 teaches the use of a plurality of thermoplastic compartments with individual heating elements in each compartment for heating water. Temperature sensors are in communication with a temperature controller to turn individual heating elements on or off to maintain the desired water temperature. The invention does not contemplate use in organic liquids, corrosive or oxidizing chemicals of high purity for which it would be unacceptable to use such heating elements. Similarly the thermoplastic compartments are relatively few in number.
U.S. Pat. No. 5,748,656 discloses the use of a metal heat-exchange system for controlling the temperature of a lasing gas in a laser system using a heat-exchanger, a temperature sensor, a microprocessor controller, and a proportioning valve to control the flow of heat exchange fluid as a way to control the temperature of the laser gas. While such an invention is useful for controlling the temperature of gases, such a heat exchange system would have limited use for controlling the temperature of liquids. This is because of the much higher heat capacity and mass of liquids compared to gases. In addition, the corrosive nature of many liquids would preclude their use by such a system. This invention does not contemplate use of the heat exchanger for dispensing of controlled temperature and volumes of liquids.
Currently it is impractical to use thermoplastic heat exchangers to control the temperature of fluids because of the high expense and large size of devices needed. Metal heat exchangers are generally unacceptable for use in semiconductor manufacturing because of the corrosive nature of the chemicals and also the need to eliminate metallic and particulate impurities from process liquids. What is needed is an apparatus for controlling and conditioning the temperature of dispensed liquid volumes or recirculating liquid systems. The system should have fast response to temperature change, be chemically inert, have high surface area, and minimal volume.